How the Moon Affects Tides

Explaining how the revolution of the moon around the Earth causes tides and why there are high tides and low tides about every twelve hours.

Do you live near a sea, river or lake? If so, then you are familiar with its regular rise and fall. The regular rise and fall of seas and other large bodies of water is called tide. Why do tides occur regularly?

The Moon and Tides.

People long ago already knew that the moon and tides are related. How did they come to know about this? People observed that the moon undergoes different phases. When there is a new moon or a full moon, they observed the water level to be high. During the first and last quarter moon, they observed the water level to be low. Just as they observed that the moon rises about less than an hour late each night, they also observed that a tide also rises about less than an hour late. These observations led the people to conclude that the moon and tides are related.

How High tides and Low Tides Occur?

Although people of long ago already associated the moon with the tides, they did not have any idea how tides occur. The first person who explained how tides occur was Sir Isaac Newton. He said that it was the moon’s gravity that causes tides. Gravity is the force which attracts an object to another object. When two objects are closer together, gravity is stronger.

The moon and the earth are relatively close together in space. They exert a strong pull on each other. The moon’s gravity pulls more strongly on the side of Earth that faces it and causes the water here to bulge. At the same time, the Earth’s center is nearer to the moon. The moon pulls Earth away from the water on this side and leaves a bulge of water behind. These areas of bulging waters have high tide. Since water has been pulled away in areas between the two high tides, these areas have low tides. The difference between a high tide and a low tide is the tidal range.

The sun also influences tides. It can strengthen or weaken the moon’s effects on earth’s water. During a new moon or full moon phase, the sun and moon are aligned with earth. The gravitational effects of the sun and moon combine. These results to high tides that are unusually high and low tides that is unusually low. These tides, called spring tides, occur twice a month. During the first or last quarter phase, the sun is at right angle to the moon. The sun’s gravitational effect reduces that of the moon. The result is a high that that is not very high and a low tide that is not very low. These tides, called neap tides, also occur twice a month.

When a tide is moving out from the shore, the water beneath the surface exerts a great pull out to sea. This force can pull large boulders or tons of sand out to sea.